Plumbing supply boxes are commonly used to connect hot and/or cold water supply lines and/or one or more waste drains to appliances and plumbing fixtures such as washing machines, icemakers, water softeners, sinks, toilets and the like. Oftentimes these boxes are molded out of a suitable thermoplastic material to enable any drain outlets to be solvent welded to thermoplastic drain pipes.
If these thermoplastic supply boxes are to be recess mounted in walls that are fire rated, the boxes must be similarly fire rated to insure that the original fire rating of the walls is maintained even though the boxes may melt and collapse inside the walls when subjected to flames or high temperatures caused by a fire. Heretofore one known way to obtain the requisite fire rating for thermoplastic supply boxes was to make the walls of the boxes thicker to better withstand heat and attach a relatively large intumescent pad to the back side of the boxes. Accordingly, should the boxes be subjected to sufficient heat to cause the boxes to melt and collapse inside the walls, the heat will also cause the intumescent material to expand sufficiently to form a hard char to seal off the wall opening previously occupied by the boxes and thereby restore the walls to the original fire rating.
A major disadvantage in using such intumescent pads to achieve the requisite fire rating for thermoplastic supply boxes is the relatively high cost of the intumescent pads and poor structural integrity of the supply boxes at high temperatures.